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Magnetic superleaks

Naturevolume 266pages824825 (1977) | Download Citation



Two new natural materials which behave as superleaks to superfluid 4He and also have magnetic properties are described here. In the search for magnetic superleaks the first choice was, obviously, a highly magnetic material such as a manufactured ferrite which has the advantage that its porosity is very uniform. We tested such a material but apparently not at a low enough temperature to be able to detect any onset point for the superfluid 4He. The pores or gap distances must be extremely small1. Second, natural magnetic materials, among which the most obvious were different types of the so-called magnetites, were tested. Two magnetites of apparently quite different origin have been tested with superfluid 4He. One from the south-east of Argentina, Province of Rio Negro about 41 °S latitude and about 30 km from the Atlantic Ocean (sample A) and another of unknown origin taken at random from the Mining Department of the University of Delft (sample B). An X-ray diffraction analysis of these two samples gave the following components: For sample A, haematite (Fe2O3) (ferromagnetic), magnetite (Fe3O4) (ferrimagnetic), mica and garnet [(Mg,Fe)3Al2(SiO4)3] (paramagnetic) and for sample B, mainly magnetite (Fe3O4) (ferrimagnetic) and chlorite, a sheet silicate [(Mg,Fe)5AlSi3O16)] (OH)8 (paramagnetic). Both samples are anisotropic aggregates and the magnetic characteristics are given at room temperature.

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    Goldschvartz, J. M. Nature 260, 557–558 (1976).

  2. 2

    Goldschvartz, J. M., Martin, E. & Blaisse, B. S. Cryogenics 10, 160–161 (1970).

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    Leggett, A. J. Rev. mod. Phys. 47, 331–414 (1975).

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  1. Department of Applied Physics, Delft University of Technology, Delft, The Netherlands



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